Nuclear fuel core, nuclear fuel cartridge, and methods of fueling and/or defueling a nuclear reactor

ABSTRACT

A portable nuclear fuel cartridge comprising a unitary support structure and a plurality of nuclear fuel assemblies that collectively form a nuclear fuel core. The nuclear fuel core is integrated into the unitary support structure to collectively form a self-supporting assemblage than can be lifted as a single unit. In another aspect, the invention is a method of fueling and/or defueling a nuclear reactor utilizing a nuclear fuel cartridge that is loaded and/or unloaded from the nuclear reactor as a single unit. In another aspect, a nuclear reactor core is provided that comprises a nuclear fuel core comprising; a plurality of first nuclear fuel assemblies, each of the plurality of first nuclear fuel assemblies having a first transverse cross-sectional configuration; and a plurality of second nuclear fuel assemblies, each of the plurality of second nuclear fuel assemblies having a second transverse cross-sectional configuration that is different than the first transverse cross-sectional configuration.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/669,428 filed Jul. 9, 2012, the entirety ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention elates generally to nuclear reactors and methodsand apparatus of fueling and defueling the same, and more specificallyto an optimized arrangement of fuel assemblies in a nuclear reactor coreand/or a portable nuclear fuel cartridge.

BACKGROUND OF THE INVENTION

A typical nuclear reactor core in a light water reactor comprisestightly packed “nuclear fuel assemblies” (also referred to as nuclearfuel bundles) of square cross section. Each nuclear fuel assembly is anassemblage of multiple “nuclear fuel rods” which are sealed hollowcylindrical metal tubes (e.g. stainless steel or zirconium alloy) packedwith enriched uranium fuel pellets and integral burnable poisonsarranged in an engineered pattern to facilitate as uniform a burningprofile of the nuclear fuel assembly (in both the axial and crosssectional/transverse directions) as possible. Heretofore, in priorsystems, each of the nuclear fuel assemblies are handled individuallyand loaded/unloaded from the stationary nuclear reactor located insidethe reactor vessel one at a time, which has proved to be a cumbersomeand time consuming process. Periodically, spent nuclear fuel assembliesare removed and unloaded on a piecemeal basis from the nuclear reactorcore, which are then placed in a spent fuel pool for temporary storage.These spent nuclear fuel assemblies are later moved from the spent fuelpool to a fuel storage facility using transport canisters (such asmulti-purpose canisters) and/or casks. New nuclear fuel assemblies arethen inserted and loaded on a piecemeal basis into the nuclear reactorcore. As can be imagined, this process requires lengthy unit refuelingoutages to complete all of the necessary nuclear fuel assemblyreplacements.

The leakage of neutrons from the periphery of the fuel core is minimizedby a so-called “reflector,” which, as its name implies, serves toreflect the outgoing neutrons back towards the core. The reflectorgirdles the core, minimizing its physical space with the peripheral fuelassemblies. The square shaped fuel assemblies however, are not conduciveto making efficient use of all available space within the corecircumscribed by the reflector leaving unused regions between the coreand reflector.

In view of the above, an improved reactor core is desirable.Additionally, improved apparatus and methods for fueling and/ordefueling nuclear reactors are also desirable.

SUMMARY OF THE INVENTION

In one aspect, an improved nuclear reactor core is provided thatutilizes nuclear fuel assemblies having two different transversecross-sectional configurations. The nuclear fuel assemblies having twodifferent transverse cross-sectional configurations are arranged in apattern that, compared to existing nuclear reactor cores, takesadvantage of peripheral corner regions that are formed between the fuelcore and the reflector cylinder (which is generally a tubular structurethat circumferentially surrounds the nuclear fuel core). In nuclearreactor cores that utilize nuclear fuel assemblies having only onecross-sectional configuration, such peripheral corner regions are leftempty as they are too small to accommodate one of the nuclear fuelassemblies. By creating the nuclear reactor with nuclear fuel assemblieshaving at least two different transverse cross-sectional configurations,nuclear fuel assemblies can be provided in these peripheral cornerspaces that were previously left empty, thereby providing a nuclearreactor core that makes optimum use of the available nuclear reactorcore space to increase the service or cycle life of the nuclear fuelsupply.

In one embodiment, the improved nuclear reactor core utilizes availablenuclear reactor core space by providing a plurality of second fuelassemblies in the heretofore empty peripheral corner regions created bya plurality of first fuel assembles, wherein the first and secondnuclear fuel assemblies have different configurations. Because thesecond nuclear fuel assemblies will typically have a smaller transversecross-section than the first nuclear fuel assemblies in certainembodiments (and thus include less fuel rods), the first nuclear fuelassemblies may be referred to as “full nuclear fuel assemblies” whilethe second nuclear fuel assemblies may be referred to as “partialnuclear fuel assemblies” for convenience. In certain embodiments, thesepartial nuclear fuel assemblies may not have control rods, although inother embodiments these partial nuclear fuel assemblies may includecontrol rods. In one exemplary embodiment, with the partial nuclear fuelassemblies installed, the resulting nuclear fuel core (which may bereferred to as a fuel assembly array if desired) may approximate anoctagon in transverse cross-section. Accordingly, in some embodiments,the full nuclear fuel assemblies may have a rectangular transversecross-sectional shape while the partial nuclear fuel assemblies may havea generally triangular transverse cross-sectional shape.

Calculations show that by adding the partial fuel assemblies, the cyclelife of the nuclear fuel core may be increased by approximately fourmonths in some embodiments. An even greater increase in the cycle life,as much as an additional four months, may be realized by coasting at areduced operating power level, say approximately 90% of normal power, inthe last few months of the cycle. This stretch power approach directlyhelps in nuclear fuel utilization (through higher burn-up). Accordingly,the partial fuel assemblies advantageously support such convenient powerstretching strategies.

In one such embodiment, the invention can be a nuclear reactor corecomprising: a reflector cylinder, a nuclear fuel core disposed withinthe reflector cylinder, the fuel assembly array comprising: a pluralityof first nuclear fuel assemblies, each of the plurality of first nuclearfuel assemblies having a first transverse cross-sectional shape; and aplurality of second nuclear fuel assemblies, each of the plurality ofsecond nuclear fuel assemblies having a second transversecross-sectional shape that is different than the first transversecross-sectional shape.

In another such embodiment, the invention can be a nuclear reactor corecomprising: a plurality of first nuclear fuel assemblies, each of theplurality of first nuclear fuel assemblies having a first transversecross-sectional configuration, the plurality of first nuclear fuelassemblies arranged in a rectilinear pattern defining peripheral cornerregions; a plurality of second nuclear fuel assemblies, each of theplurality of second nuclear fuel assemblies having a second transversecross-sectional configuration that is different than the firsttransverse cross-sectional configuration; and wherein the plurality ofsecond nuclear fuel assemblies are disposed within the corner regions,the plurality of first and second nuclear fuel assemblies collectivelyforming a nuclear fuel core.

In a further such embodiment, the invention can be a nuclear fuel corecomprising: a plurality of first nuclear fuel assemblies, each of theplurality of first nuclear fuel assemblies having a first transversecross-sectional configuration; and a plurality of second nuclear fuelassemblies, each of the plurality of second nuclear fuel assemblieshaving a second transverse cross-sectional configuration that isdifferent than the first transverse cross-sectional configuration.

In another aspect, a portable nuclear fuel cartridge is provided thatallows a nuclear reactor to be completely fueled and/or defueled byloading and/or unloading a self-supporting assemblage as a single unit.The portable nuclear fuel cartridge includes a unitary support structureand an integrated nuclear fuel core that is configured to be insertableinto and removable from a nuclear reactor vessel as a self-contained andself-supporting unit, thereby forming a complete and highly portablenuclear fuel core. Accordingly, embodiments of the present inventioninclude a portable nuclear fuel cartridge which is self-supporting andfree standing outside of the nuclear reactor vessel with all of thenuclear fuel assemblies completely pre-installed. The integrated nuclearfuel core may comprise all of the nuclear fuel assemblies required tooperate the nuclear reactor.

Without limitation, the portable nuclear fuel cartridge may comprise aunitary support structure, such as an open skeletal framework, thatsupports the nuclear fuel core therein. The unitary support structuremay be comprised of top and bottom support structures, such as top andbottom core plates, that are coupled together by connecting members,such as rods. The nuclear fuel core is retained in the unitary supportstructure and sandwiched between the top and bottom support structure.In one embodiment, a reflector such as a reflector cylinder may beincluded as part of the portable nuclear fuel cartridge. In otherembodiments, the reflector may be omitted as the reflector may beincluded as part of the nuclear reactor vessel.

The portable nuclear fuel cartridge may be preassembled outside of thenuclear reactor vessel with all nuclear fuel assemblies intact, and theninserted into the nuclear reactor vessel. When the fuel supply isdepleted, the entire portable nuclear fuel cartridge may be readilyremoved from the nuclear reactor vessel and a new complete andpreassembled portable nuclear fuel cartridge may be inserted in itsplace. Advantageously, this negates the need to handle individualnuclear fuel assemblies on-site in piecemeal fashion to significantlyreduce nuclear unit downtime for refueling. The portable nuclear fuelcartridge is constructed to be lifted, transported, installed, andstored as self-supporting and free-standing. In essence, the portablenuclear fuel cartridge serves as a “cradle-to-grave” structure fromfueling a nuclear reactor to long-term storage.

In one such embodiment, the invention can be a portable nuclear fuelcartridge comprising: a unitary support structure; a plurality ofnuclear fuel assemblies arranged to collectively form a fuel core for anuclear reactor, each of the plurality of nuclear fuel assembliescomprising a plurality of nuclear fuel rods; and the fuel coreintegrated into the unitary support structure to collectively form aself-supporting assemblage than can be lifted as a single unit.

In another such embodiment, the invention can be a portable nuclear fuelcartridge configured for placement in a reactor vessel, the fuelcartridge comprising: top and bottom core plates at opposing ends of theunitary nuclear fuel cartridge, each of the top and bottom core platesincluding a gridwork defining a plurality of open cells; a plurality ofnuclear fuel assemblies disposed between the top and bottom core plates,each of the plurality of nuclear fuel assemblies including a pluralityof fuel rods; a plurality of connecting members extending between andinterconnecting the top and bottom core plates together to form aunitary support structure; and the top and bottom core plates, theplurality of connecting members, and the plurality of nuclear fuelassemblies collectively defining an assemblage that is self-supportingoutside of the reactor vessel and transportable as a single unit.

In a further such embodiment, the invention can be a method ofassembling a nuclear fuel cartridge comprising: a) positioning aplurality of fuel assemblies between top and bottom core plates, eachfuel assembly including a plurality of fuel rods and top and bottom flownozzles at opposing ends thereof: b) coupling the top and bottom coreplates together with a plurality of connecting rods extending betweenthe core plates; and c) drawing the top and bottom core plates togetherwith the connecting rods, wherein the fuel assemblies are sandwichedbetween the top and bottom core plates to form a self-supportingassemblage than can be lifted as a single unit.

In a further aspect, methods of fueling and/or defueling a nuclearreactor are provided that take advantage of a nuclear fuel cartridgethat comprises a unitary support structure and a nuclear fuel coreintegrated into the unitary support structure such that the nuclear fuelcartridge can be handled as a single unit.

In one such embodiment, the invention can be a method of fueling anuclear reactor, the method comprising: a) opening a nuclear reactorvessel; b) moving a nuclear fuel cartridge from a position outside ofthe nuclear reactor vessel to a position within an interior cavity ofthe nuclear reactor vessel, the nuclear fuel cartridge comprising aunitary support structure, and a plurality of nuclear fuel assembliesarranged to collectively form a fuel core, the fuel core mounted in theunitary support structure; and c) closing the nuclear reactor vessel.

In another such embodiment, the invention can be a method of defueling anuclear reactor, the method comprising: a) opening a nuclear reactorvessel; b) removing a nuclear fuel cartridge from an interior cavity ofthe nuclear reactor vessel, the nuclear fuel cartridge comprising aunitary support structure, and a plurality of nuclear fuel assembliesarranged to collectively form a fuel core, the fuel core mounted in theunitary support structure; and c) submerging the nuclear fuel cartridgewithin a spent fuel pool.

In yet another such embodiment, the invention can be a method of storingspent nuclear fuel, the method comprising: a) removing a nuclear fuelcartridge from an interior cavity of the nuclear reactor vessel, thenuclear fuel cartridge comprising a unitary support structure, and aplurality of nuclear fuel assemblies arranged to collectively form afuel core, the fuel core mounted in the unitary support structure; b)positioning the nuclear fuel cartridge in a multi-purpose canister; andc) positioning the multi-purpose canister in a cask.

It is to be understood that the various aspects of the inventiondescribed above can be combined in various manners. Moreover, furtherareas of applicability of the present invention will become apparentfrom the detailed description provided hereinafter. It should beunderstood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the exemplary embodiments will be described withreference to the following drawings in which like elements are labeledsimilarly, and in which:

FIG. 1 is a perspective view of a nuclear fuel cartridge according to anembodiment of the present invention;

FIG. 2 is an exploded view of the nuclear fuel cartridge of FIG. 1;

FIG. 3 is a transverse cross-sectional view through the nuclear fuelcartridge of FIG. 1;

FIG. 4 is transverse cross-sectional view through a nuclear fuel coreaccording to an embodiment of the present invention, which happens to beincorporated into the nuclear fuel cartridge of FIG. 1;

FIG. 5A is a perspective view of a first nuclear fuel assembly having afirst transverse cross-sectional configuration removed from the nuclearfuel core of FIG. 4, the first transverse cross-sectional configurationcomprising a rectangular transverse cross-sectional shape asexemplified;

FIG. 5B is a perspective view of a second nuclear fuel assembly having asecond transverse cross-sectional configuration removed from the nuclearfuel core of FIG. 4, the second transverse cross-sectional configurationcomprising a triangular transverse cross-sectional shape as exemplified;

FIG. 6 is a close-up view of the top portion of the first nuclear fuelassembly of FIG. 5B taken at area VI;

FIG. 7 is a close-up view of the top and bottom portions of the firstnuclear fuel assembly of FIG. 5B, wherein the first nuclear fuelassembly is shown broken in length;

FIG. 8 is a top view of the first nuclear fuel assembly of FIG. 5B;

FIG. 8 is a bottom view of the first nuclear fuel assembly of FIG. 5B;

FIG. 10 is a perspective view of a unitary support structure of thenuclear fuel cartridge of FIG. 1, wherein the nuclear fuel core andreflector cylinder have been removed;

FIG. 11 is a side view of the unitary support structure of FIG. 10;

FIG. 12 is a top view of the unitary support structure of FIG. 10;

FIG. 13 is a bottom view of the unitary support structure of FIG. 10;

FIG. 14 is a perspective view of a bottom core plate of the unitarysupport structure of FIG. 10;

FIG. 15 is a close-up view of the top portion of one of the arcuatesegments of the reflector cylinder of the nuclear fuel cartridge of FIG.1;

FIG. 16 is a side view of the nuclear fuel cartridge of FIG. 1positioned within a nuclear reactor vessel, in accordance with anembodiment of the present invention;

FIG. 17-24 schematically illustrate a method of defueling a nuclearreactor according to an embodiment of the present invention, wherein thenuclear fuel cartridge of FIG. 1 has been used to operate the nuclearreactor; and

FIG. 25-36 schematically illustrate a method of defueling a nuclearreactor according to an embodiment of the present invention, wherein thenuclear fuel cartridge of FIG. 1 has been used to operate the nuclearreactor.

All drawings are schematic and not necessarily to scale. Parts given areference numerical designation in one FIGURE may be considered to bethe same pans where they appear in other figures without a numericaldesignation for brevity unless specifically labeled with a differentpart number and described herein

DETAILED DESCRIPTION

The features and benefits of the present disclosure are illustrated anddescribed herein by reference to exemplary embodiments. This descriptionof exemplary embodiments is intended to be read in connection with theaccompanying drawings, which are to be considered part of the entirewritten description. Accordingly, the present disclosure expresslyshould not be limited to such embodiments illustrating some possiblenon-limiting combination of features that may exist alone or in othercombinations of features; the scope of the claimed invention beingdefined by the claims appended hereto.

In the description of embodiments disclosed herein, any reference todirection or orientation is merely intended for convenience ofdescription and is not intended in any way to limit the scope of thepresent invention. Relative terms such as “lower,” “upper,”“horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and“bottom” as well as derivative thereof (e.g., “horizontally,”“downwardly,” “upwardly,” etc.) should be construed to refer to theorientation as then described or as shown in the drawing underdiscussion. These relative terms are for convenience of description onlyand do not require that the apparatus be constructed or operated in aparticular orientation. Terms such as “attached,” “coupled,” “affixed,”“connected,” “interconnected,” and the like refer to a relationshipwherein structures are secured or attached to one another eitherdirectly or indirectly through intervening structures, as well as bothmovable or rigid attachments or relationships, unless expresslydescribed otherwise.

For ease of discussion, the descriptions of the various aspects of theinvention have been broken down into three sections. It is, however, tobe understood that in certain embodiments, the aspects of theinventions, or portions thereof, can be combined as desired. Forexample, the optimized fuel core concepts discussed in the first sectionbelow can be included in the portable nuclear fuel cartridge conceptdiscussed in the second section discussed below, and vice versa. Inother embodiments, however, the optimized fuel core concepts are notlimited to the portable nuclear fuel cartridge environment but can beincorporated into a nuclear reactor core having a stationary supportstructure for supporting the nuclear fuel assemblies in the optimizedfuel core arrangement. Similarly, while the portable nuclear fuelcartridge is exemplified as utilizing the optimized fuel core in certainembodiments, in other embodiments the portable nuclear fuel cartridgecan utilize a nuclear fuel core with a more traditional pattern, such asa rectilinear arrangement that utilizes only nuclear fuel assemblieshaving the same transverse cross-sectional configuration.

Optimized Fuel Core Geometry & Reactor Core Including the Same

Referring first to FIG. 4, a nuclear fuel core 100 according to anembodiment of the present invention is illustrated. In certainembodiments, the nuclear fuel core 100 can be incorporated into aportable nuclear fuel cartridge 1000 (discussed in greater detailbelow), which is then positioned within a nuclear reactor vessel 500,thereby forming a nuclear reactor core 550 in conjunction with otherreactor core infrastructure and stationary components. In anotherembodiment, the nuclear fuel core 100 can be formed in the nuclearreactor vessel 500 by loading the nuclear fuel assemblies 110, 120 intoa stationary support structure that is designed to create the optimizedfuel arrangement discussed below, thereby forming the nuclear reactorcore.

The nuclear fuel core 100 comprises a plurality of first nuclear fuelassemblies 110 and a plurality of second nuclear fuel assemblies 120.Each of the plurality of first nuclear fuel assemblies 110 comprises afirst transverse cross-sectional configuration. Each of the plurality ofsecond nuclear fuel assemblies 120 comprises a second transversecross-sectional configuration, wherein the first and second transversecross-sectional configurations are different from one another. In oneembodiment, the first transverse cross-sectional configuration isdifferent than the second transverse cross-sectional configuration dueto the first and second transverse cross-sectional configurations beingdifferent shapes. In another embodiment, the first transversecross-sectional configuration is different than the second transversecross sectional configuration due to the first and second transversecross-sectional configurations being different sizes. In certain otherembodiments, the first transverse cross-sectional configuration isdifferent than the second transverse cross sectional configuration dueto the first and second transverse cross-sectional configurations beingof different sizes and shapes.

In the exemplified embodiment, the first transverse cross-sectionalconfiguration of the first nuclear fuel assemblies 110 comprises arectangular transverse cross-sectional shape while the second transversecross-sectional configuration of the second nuclear fuel assemblies 120comprises a triangular transverse cross-sectional shape. In oneembodiment, the rectangular transverse cross-sectional shape of thefirst transverse cross-sectional configuration of the first nuclear fuelassemblies 110 is square. The invention, however, is not limited to anyspecific shape for either of the first and/or second transversecross-sectional configurations unless specified by the claims. In otherembodiments, the first and/or second transverse cross-sectionalconfigurations can take on other polygonal, oval, and/or irregularshapes.

In another embodiment, both the first and second transversecross-sectional shapes can comprises a rectangular transversecross-sectional shapes, wherein the rectangular transversecross-sectional shape of the second transverse cross-sectionalconfiguration has a sufficiently smaller area than that of therectangular transverse cross-sectional shape of the first transversecross-sectional configuration such that the second plurality of nuclearfuel assemblies 120 can fit within the peripheral corner regions 101 (asexplained in greater detail below).

The plurality of first nuclear fuel assemblies 110 are arranged to forma central region of the nuclear fuel core 100 while the second nuclearfuel assemblies 120 are arranged about the periphery of the centralregion formed by the first nuclear fuel assemblies 110. In theexemplified embodiment, the plurality of first nuclear fuel assemblies110 are arranged in a rectilinear pattern to form a central regionhaving a modified cruciform shape defining peripheral corner regions112. In one embodiment, such as the one illustrated, the modifiedcruciform pattern formed by the first nuclear fuel assemblies 120comprises four symmetric quadrants, each of the four quadrantscomprising two peripheral corner regions 112. Of course, in otherembodiments, the first nuclear fuel assemblies 110 can be arranged inother patterns, rectilinear or non-rectilinear, that also formperipheral corner regions 112.

The plurality of second nuclear fuel assemblies 120 are disposed withinthe corner regions 112, thereby forming a nuclear fuel core 100 that isdensely packed with fuel assemblies 110, 120 that maximizes theavailable space in the nuclear reactor core (which in some embodimentsmay be defined as the space circumscribed by the reflector cylinder140). Moreover, while in the exemplified embodiment, the nuclear fuelcore 100 comprises nuclear fuel assemblies 110, 120 having two differenttransverse cross-sectional configurations, in other embodiments thenuclear fuel core 100 may comprise nuclear fuel assemblies having morethan two different transverse cross-sectional configurations, such asthree or four to further maximize the available space in the nuclearreactor core.

Due to the arrangement of the second nuclear fuel assemblies 120 in thecorner regions 112 formed by the pattern of the first nuclear fuelassemblies 110, the nuclear fuel core 100 has a polygonal transversecross-sectional shape. In one non-limiting embodiment, when the firstand second nuclear fuel assemblies 110, 120 are arranged in theillustrated pattern, the nuclear fuel core 100 has an octagonaltransverse cross-sectional shape. Of course, other transversecross-sectional shapes can be achieved for the nuclear fuel core 100utilizing the above concepts, the exact shape of which will be dictatedby the selected transverse cross-sectional shapes of the first andsecond nuclear fuel assemblies 110, 120 and their arrangement within thepattern.

In one example, without limitation, the nuclear fuel core 100 may becomprised of thirty-seven full first nuclear fuel assemblies 110 andeight second nuclear fuel assemblies 120. Due in part to its smalltransverse cross-section compared to large nuclear reactor cores, acompact nuclear fuel core 100 with thirty-seven first nuclear fuelassemblies 110 enriched to 5% U-235 computes to have a cycle life ofapproximately 42 months (in contrast to only 18 to 24 months for thelarge reactor cores used in modern operating reactors).

In one embodiment, each of the thirty-seven first nuclear fuelassemblies 110 in this nuclear fuel core 100 include their ownindividual control rod assembly that is operated autonomously to raiseand/or lower control rods 150 (best shown in FIG. 7) to controlreactivity during the nuclear reactor's operation. Each of the pluralityof second nuclear fuel assemblies 120 is free of a control rod assemblyin one embodiment. However, in other embodiments, each of the pluralityof second nuclear fuel assemblies 120 can include a control rod assemblysimilar to that described above for the first nuclear fuel assemblies100.

Each of the first and second nuclear fuel assemblies 110, 120 comprise aplurality of nuclear fuel rods 111. Because the first nuclear fuelassemblies 110 are larger in transverse cross-sectional size than thesecond nuclear fuel assemblies 120, each of the plurality of firstnuclear fuel assemblies 110 comprises X nuclear fuel rods while each ofthe plurality of second nuclear fuel assemblies 120 comprises Y nuclearfuel rods, wherein Y is less than X. Thus, conceptually, the firstnuclear fuel assemblies 110 may be referred to as “full nuclear fuelassemblies” while the second nuclear fuel assemblies 120 may be referredto as “partial nuclear fuel assemblies” for convenience. In oneembodiment, a ratio of Y:X is in a range of 1:1.5 to 1:3. In a morespecific embodiment, Y is about one-half X.

Referring now to FIGS. 4 and 16 concurrently, it is mentioned above thatwhen the nuclear fuel core 100 is properly positioned in (or formedwithin) an interior cavity 515 of the nuclear reactor vessel 500, anuclear reactor core 550 is conceptually formed. In certain embodiments,in addition to the nuclear fuel core 100, the nuclear reactor core 550may comprises a reflector cylinder. While in the embodiment illustratedin FIG. 16 the reflector cylinder is integrated as part of the nuclearfuel cartridge 1000 (see element 140 in FIG. 2), in other embodiments,the reflector cylinder may be mounted within the nuclear reactor vessel500 in a stationary manner.

Irrespective of whether the reflector cylinder is part of a portablenuclear fuel cartridge or permanently mounted within the nuclear reactorvessel 500, the reflector cylinder may be a hollow tubular structurewhich extends vertically and defines a substantially circular interiorcompartment (in transverse cross-section) in which the nuclear fuel core100 is disposed. The reflector cylinder minimizes leakage of neutronsfrom the periphery of the nuclear fuel core 100 by reflecting theoutgoing neutrons back towards the nuclear fuel core 100. The reflectorcylinder circumferentially surrounds the nuclear fuel core 100. In oneembodiment, the reflector cylinder may be comprised of individualarcuately-shaped reflector wall segments, as described in greater detailbelow for the portable nuclear fuel cartridge 1000. In otherembodiments, the reflector cylinder is singular hollow tube structure.

In certain embodiments, the reflector cylinder has a circular transversecross-sectional shape while the first nuclear fuel assemblies 110 have arectangular transverse cross-sectional shape and are arranged in arectilinear pattern. As a result, a spaces exists between the peripheryof the pattern of first nuclear fuel assemblies 110 and the innersurface of the reflector cylinder that is too small (or of a shape) suchthat one of the first nuclear fuel assembly cannot be accommodated.However, due to having a different transverse configuration than that ofthe first nuclear fuel assemblies 110, the second nuclear fuelassemblies 110 can be accommodated within the spaces formed between theperiphery of the pattern of first nuclear fuel assemblies 110 and theinner surface of the reflector cylinder. In one embodiment, the shapeand size of the transverse cross-sectional shape of the second nuclearfuel assemblies 120 is selected so that the spaces between the peripheryof the pattern of first nuclear fuel assemblies 110 and the innersurface of the reflector cylinder are substantially filled andcompletely occupied. As a result, the nuclear fuel core 100 allowsadditional nuclear fuel rods 111 to be packed into the nuclear fuel core100 while not taking up additional space within the nuclear reactorvessel 500.

Additional structural details of certain embodiments of the first andsecond fuel assemblies 110, 120 will be described below with respect tothe portable nuclear fuel cartridge 1000.

Portable Nuclear Fuel Cartridge

Referring now to FIGS. 1-3 concurrently, a portable nuclear fuelcartridge 1000 according to an embodiment of the present invention isillustrated. The portable nuclear fuel cartridge 1000 is a unitary,self-supporting construction that, in certain embodiments, can befree-standing when position on a horizontal surface. As discussed ingreater detail below, the portable nuclear fuel cartridge 1000 comprisesa unitary support structure 200 (shown in isolation in FIG. 10) and anintegrated nuclear fuel core, which is exemplified as the nuclear fuelcore 100 discussed above. While the nuclear fuel core 100 isparticularly suited for use in the portable nuclear fuel cartridge 1000,it should be noted that the portable nuclear fuel cartridge 1000 caninclude a wide variety of nuclear fuel core arrangements and, in certainembodiments, is not limited to the arrangement particulars of thenuclear fuel core 100 described above. For example, in one suchembodiment, the portable nuclear fuel cartridge 1000 can utilize anuclear fuel core that includes only one type of nuclear fuel assembly,such as only the first fuel assemblies 1000 (or other types of fuelassemblies, such as hexagonal)

The portable nuclear fuel cartridge 1000, which includes an integratednuclear fuel core 100 can be lifted and transported as a self-containedand self-supported structural unit. This allows for rapid fueling (whichas used herein includes refueling) and defueling of the nuclear reactorvessel 500. Conceptually, the portable nuclear fuel cartridge 1000 maysimply be plugged into or unplugged from a reactor vessel somewhatanalogous to a self-contained power source like a typical battery. Duein part to the unitary construction of the portable nuclear fuelcartridge 1000 (with complete nuclear fuel core contained therein), theentire refueling outage duration for a nuclear reactor can be reduced to5 days compared to a 30-day outage duration of modern reactors. Combinedwith a 48-month operating cycle, a nuclear reactor utilizing theportable nuclear fuel cartridge 1000 computes to have an installedavailability factor of 99.6% (1455 days out of 1460 days), which hasbeen unattainable heretofore in modern day reactors.

As exemplified, the portable nuclear fuel cartridge 1000 generallycomprises the unitary support structure 200 (shown in isolation in FIG.10), the nuclear fuel core 100 and a reflector cylinder 140. In certembodiments, the reflector cylinder 140 may be omitted and incorporatedinto the nuclear react vessel 500 as described above. The nuclear fuelcore 100 is mounted within the unitary support structure 200 (describedin greater detail below) such that a self-supporting assemblage iscollectively formed than can be lifted as a single unit.

Referring now to FIGS. 1-3 and 10-14 concurrently, the unitary supportstructure 200 is illustrated according to one embodiment of the presentinvention. The unitary support structure 200 is sufficiently strong toenable handling of the portable nuclear fuel cartridge 1000 within amargin of safety required by ANSI 14.6 (1993). While a specificstructural embodiment of the unitary support structure 200 will bedescribed below, it is to be understood that the unitary supportstructure 200 can take on wide variety of structural embodiments andconfigurations, including skeletal frameworks and enclosure-likehousings.

The unitary support structure 200 generally comprises a bottom supportstructure 230 (exemplified as a bottom core plate), a top supportstructure 232 (exemplified as a top core plate), and a plurality oflongitudinal members 234, 236 (exemplified as connecting rods) thatinterconnect the top and bottom support structures 232, 230. It is to beunderstood that while the top and bottom structures are referred to astop and bottom core plates herein, it is to be understood that theseterms are used broadly to encompass any structure that can provide therequisite structural integrity for handling the load while allowingadequate fluid flow through the integrated nuclear fuel core 100.

The nuclear fuel core 100 is sandwiched between the top and bottom coreplates 232, 230 so as to be incapable of being removed from the unitarysupport structure 200 without disassembling the unitary supportstructure 200. As can be seen each of the top and bottom core plates232, 230 comprise a lattice structure (or gridwork) 201 that defines aplurality of open cells 215. Thus, each of the top and bottom coreplates 232, 230 comprises a plurality of open cells 215.

The bottom and top core plates 130, 132 are each a honeycomb latticestructure, which has minimum cross sectional area and weight, butmaximum flexural strength. This provides maximum open area for fluidflow in the vertical/axial direction. The resistance to flow can becustomized by adding additional hydraulic resistance under each nuclearfuel assembly 110, 120 of the nuclear fuel core 100 to promote thedesired distribution of water up-flow along and through each fuelassembly 110, 120 in the nuclear fuel core 100. As described in greaterdetail below, each of the plurality of open cells 215 of the top andbottom core plates 232, 230 fluidly communicate with at least one of thenuclear fuel assemblies 110, 120 of the nuclear fuel core 100 to form afluid flow path through the nuclear fuel assemblies 110, 120.

While the bottom core plate 130 is depicted in FIG. 14, it is to beunderstood that the top core plate 132 may have a similar construction.Thus, the description below is applicable to both the bottom and topcore plates 232, 230. The lattice/gridwork 201 is formed created by anarray of intersecting grid plates 255 that are supported within anannular rim 256. The plurality of open cells 215 are created by thearray of intersecting grid plates 255. The open cells 215 definepassageways which are each configured and dimensioned to conform to theconfiguration of a respective one of the first or second nuclear fuelassemblies 110, 120 that are aligned therewith. When installed in thenuclear reactor during operation, this forms a primary reactor coolantflow paths through the portable nuclear fuel cartridge 1000 (inconjunction with the top and bottom nozzles 152, 154 of the fuelassemblies). Accordingly, the open cells 215 may each have a polygonalconfiguration in top plan view in one embodiment which coincides with anassociated nuclear fuel assembly 110, 120. Thus, in one embodiment, theopen cells 215 intended for the first nuclear fuel assemblies 110 may besquare in configuration while the open cells 215 intended for the secondnuclear fuel assemblies 120 may be triangular in configuration. Theseopen cells 215 are arranged in pattern that corresponds to the patternformed by the first and second nuclear fuel assemblies 110, 120 of thenuclear fuel core 100. In one arrangement, the triangular shaped opencells 215 are located near the periphery of the top and bottom coreplates 232, 230. In the exemplified embodiment, the open cells 115collectively form a pattern having an octagonal shape in top plan viewthat matches the nuclear fuel core 100.

Turning back to the structure of the unitary support structure 200, theplurality of longitudinal members 134, 136 interconnect the top andbottom core plates 232, 230 at a fixed distance from one another. In theexemplified embodiment, the longitudinal members comprise a plurality ofconnecting rods 234, 236 extending axially between the top and bottomcore plates 232, 230. As exemplified, the plurality of connecting rodscomprise a plurality of peripheral connecting rods 234 located outboardof the nuclear fuel core 100 and a plurality of central connecting rods236 located inboard of the nuclear fuel core 100.

The plurality of peripheral connecting rods 234 are circumferentiallyarranged around a periphery of the self-supporting assemblage formed bythe combination of the unitary support structure 200 and the nuclearfuel core 100. In the exemplified embodiment, the plurality ofperipheral connecting rods 234 are circumferentially arranged around theperiphery in a substantially equi-spaced arrangement. The peripheralconnecting rods 234 extend through mounting holes 251 formed through andaround the periphery of the top and bottom core plates 232, 230 (in theannular rim 256). As discussed below, the holes 251 are concentricallyalignable with through-passageways 144 of the reflector cylinder 140 sothat the peripheral connecting rods 234 can be used to coupled thereflector cylinder 140 to the unitary support structure 200.

The plurality of central connecting rods 236 are located adjacent acentral axis A-A of the self-supporting assemblage formed by thecombination of the unitary support structure 200 and the nuclear fuelcore 100. The central connecting rods 236 pass through the space createdby modifying the corners of the centrally located open cells 215 of bothof the top and bottom core plates 232, 230. The first nuclear fuelassembly 110 positioned mounted in the central cells 215 of the top andbottom core plates 232, 230 is modified to include notches in itscorners to accommodate the plurality of central connecting rods 236. Thecentral cell 215 includes corner brackets 253 formed in each of the fourcorners at the intersections of the grid plates 155. The brackets 253include holes configured to pass the central connecting rods 234therethrough. The centrally connecting rods 134 help ameliorate thebending stress in the bottom core plate 230, which carries the deadweight of the nuclear fuel core 100 during lifting and handling of theportable nuclear fuel cartridge 1000 for various operations. In someembodiments, however, the central connecting rods 156 may be omitted.

In one embodiment, the top and bottom core plates 232, 230 may becoupled together using the connecting rods 134, 136 with suitablemounting hardware 260. The mounting hardware 260 may include washers andhex nuts configured to engage threaded ends of the connecting rods 234,236. Other suitable mounting hardware or means to couple the bottom andtop core plates 230 232 may be used, such as welding. In one embodiment,the top and bottom core plates 232, 230 are removably coupled togetherto allow the nuclear fuel cartridge 100 to be removed.

In one embodiment, the unitary support structure 200 may further includean integral lifting ring 270 to facilitate lifting and handling of theportable nuclear fuel cartridge 1000, such as by a crane and/or withappropriate rigging. In on embodiment, the lifting ring 270 is fastenedor otherwise fixed to the top core plate 232. Any suitable means ofconnection could be used. In one possible embodiment, the peripheralconnecting rods 234 that join the top and bottom core plates 232, 230together using mounting hardware 260 may be used to attach the liftingring 270 to the top core plate 232. Other suitable attachments methodsmay be used in addition to or instead of using the peripheral connectingrods 234, such as welding, fasteners, or the like. The foregoing areonly some possible, non-limiting examples.

Referring now to FIGS. 1-3 and 15, the portable nuclear fuel cartridge1000 may also include, in certain embodiments, a reflector cylinder 140coupled to the unitary support structure. The reflector cylinder 140 maybe a hollow tubular walled structure which extends vertically anddefines a substantially circular interior compartment (in transversecross-section) for enclosing the nuclear fuel core 100.

In one embodiment, the reflector cylinder 140 may be comprised ofindividual arcuately-shaped reflector wall segments 141 which arecircumferentially joined together by longitudinally-extending flangedjoints 146 formed by vertical flanges 148 formed on each lateral side149 of a segment. In one embodiment, the flanged joints 146 formedbetween adjoining reflector wall segments 141 may be interlocking lapjoints in design having a step-shaped joint configuration as shown sothat a portion of each segment lateral side 149 overlaps the lateral endof the adjacent reflector segment to eliminate any straight pathwaysthrough the reflector cylinder 140 for neutrons to escape. Various othersuitable configurations are possible. As noted herein, the reflectorcylinder 140 reflects the neutrons escaping from the nuclear fuel core100 back inwards towards the nuclear fuel core 100. The reflector wallsegments 141 of reflector cylinder 140 may be made of any suitablemetallic material operable having neutron reflecting properties.

The reflector cylinder 140 can be coupled to the unitary supportstructure 200 in a variety of manners, such as fastening, welding, orinterference fit. In on embodiment, the reflector cylinder 140 iscoupled to the unitary support structure 200 using the peripheralconnecting rods 234 that also join the bottom and top plates 230, 232.In this embodiment, the peripheral connecting rods 234 pass throughlongitudinally-extending passageways 144 formed in each reflector wallsegment 141. In the exemplified embodiment, the longitudinally-extendingpassageways 144 are located on flanges that protrude inward from thereflector wall segment 141.

As mentioned above, the peripheral connecting rods 234 also extendthrough the mounting holes 251 formed through and around the peripheryof the top and bottom core plates 232, 230 in the annular rim 256. Theholes 251 are axially alignable with through passageways 144 of thereflector wall segments 141 to pass the connecting rods 234therethrough. The flanged joints 146 between adjoining reflector wallsegments 141 in some embodiments may be held together by the foregoingassembly of the bottom and top core plates 230, 232 and the peripheralconnecting rods 234 without any direct mechanical coupling between theflanges 148 of the reflecting segments.

When coupled to the unitary support structure 200, the reflectorcylinder 140 circumscribes the nuclear fuel core 100. In someembodiments, the reflector cylinder 140 may be omitted from the portablenuclear fuel cartridge 1000.

Referring now to FIGS. 5A and 6-9 concurrently, a single one of thefirst fuel assemblies 110 is illustrated. Each first fuel assembly 110includes a plurality of fuel rods 111, longitudinally spaced grid sheets113 (that include a plurality of openings through which the plurality offuel rods 111 extend), a plurality of control rods 150, a top nozzle152, and a bottom nozzle 154. The top and bottom nozzles 152, 154 aredisposed at opposing top and bottom ends 157, 158 of the first nuclearfuel assembly 110. In one embodiment, the top and bottom nozzles 152,154 are open structures defining a central flow opening and may beformed by adjoining peripheral plates having a polygonal configurationin top plan view, and in some embodiments a rectilinear configuration.

In one embodiment, the top and bottom flow nozzles 152, 154 areconfigured and dimensioned to engage the top and bottom core plates 130,132 respectively of the portable nuclear fuel cartridge 1000 so that thefirst nuclear fuel assemblies 110 cannot be completely passed throughthe open cells 215 of the top and bottom core plates 232, 230. Thoughtof another way, each of the plurality of fuel assemblies 110, 120 aresized and/or shaped so as to be incapable of being removed from theunitary support structure 200 through the open cells 215 of the top andbottom core plates 232, 230 with which it is in fluid communication.This allows the first nuclear fuel assemblies 110 to be removably lockedinto the top and bottom core plates 232, 230 when the portable nuclearfuel cartridge 1000 is being assembled.

Accordingly, in one embodiment, each of the nuclear fuel assemblies 110,120 comprises a top portion (which in the exemplified embodimentcomprises the top nozzle 152) that at least partially nests within oneof the plurality of open cells 215 of the top core plate 232 and abottom portion (which in the exemplified embodiment comprises the bottomnozzle 154) that at least partially nests within one of the plurality ofopen cells 215 of the bottom core plate 230. In embodiments where thetop and bottom nozzles 152, 154 may be omitted other cap or sleevestructures could be used in their stead.

Furthermore in order to ensure that the nuclear fuel assemblies 110, 120cannot be completely passed through the open cells 215 of the top andbottom core plates 232, 230, the top portion of each of the nuclear fuelassemblies 110, 120 comprises a top shoulder element (exemplified asstepped portion 180) that abuts a bottom surface of the top core plate232. Similarly, the bottom portion of each of the nuclear fuelassemblies 110, 120 comprises a bottom shoulder element (alsoexemplified as stepped portion 180) that abuts a top surface of thebottom core plate 230. In other embodiments, the top and/or bottomshoulder elements can take the form of a protuberance, pin, flange, orany other structure capable of mechanically interfering with the latticestructure/gridwork 201 in a manner that prevents the nuclear fuelassemblies 110, 120 from being slid completely through the open cells215. In still another embodiment, top and/or bottom shoulder elementscan be formed by a sloped section/wall of the nuclear fuel assemblies110, 120.

The top nozzle 152 and the bottom nozzle 154 each include the steppedportion 180 which, as mentioned above, is configured to engage the gridplates 255 defining the open cells 215 of the top and bottom core plates232, 230, thereby preventing the fuel assemblies 110, 120 from passingcompletely through the open cells 215 in which they nest. In theexemplified embodiment, the stepped portion 180 is formed in theperipheral lateral sides 181 of each flow nozzle 152, 154. The steppedportion 180 may extend partially or completely around the perimeter ofthe sides 181 of the top and bottom nozzles 152, 154 and be intermittentor continuous in configuration. The stepped portion 180 of top andbottom nozzles 152, 154 defines an outer insertion end portion 182configured to extend at least partially into the open cells 115 of thebottom and top core plates 230, 232 and an inner end portion 183configured to have a larger cross sectional width than the open cells215 so as to remain outside of the open cells 215 when the insertion endportion 182 of the top and bottom nozzles 152, 154 are inserted into theopen cells 215.

As opposed to prior reactor core arrangements wherein the core platesare permanently affixed inside the reactor vessel and the fuelassemblies must be individually inserted one at a time through openingsin the fixed plates, the foregoing present arrangement and configurationof the bottom and top core plates 230, 232 and top and bottom flownozzles 152, 154 advantageously permit the fuel assemblies 110, 120 tobe compressed between the top and bottom core plates 232, 230 to form aself-supporting and free standing structure.

In some embodiments, the top and bottom nozzles 152, 154 may furtherhave a transverse cross-sectional shape which complements thecross-sectional shape of the first fuel assembly 110. In one embodiment,the top and bottom nozzles 152, 154 may have a square shape in top planview. The top and bottom nozzles 152, 154 provide flow outlets andinlets for the nuclear fuel core 100, allowing the reactor primarycoolant to flow through the core 100 from end to end and pick up heatfrom the fuel rods 111.

As shown in FIG. 5B, the second nuclear fuel assemblies 120 may besimilar in construction to the first fuel assemblies 110 describedabove, having fuel rods 111, top and bottom nozzles 152, 154, controlrods 150, and grid sheets 113. The exception being that the componentshave a three-sided configuration instead of a four-sided configuration.

Having described the structure of the portable nuclear fuel cartridge1000, an exemplary method for assembling the portable nuclear fuelcartridge 1000 will now be briefly described. The assembly process maybegin by first generally positioning the fuel assemblies 110, 120between top and bottom core plates 232, 230. The flow nozzles 252, 254of the fuel assemblies 110, 120 are axially aligned with a respectiveopen cell 215 in the top and bottom core plates 232, 230. Next, theprocess includes partially inserting the insertion end portion 182 ofthe top flow nozzle 152 of each of the fuel assemblies 110, 120 into anopen cell 215 formed in the top core plate 232. This is done in oneembodiment from the underside of the top core plate 232. The top nozzle152 is now partially inserted into the open cell 215 and the shoulderportion 180 of the top nozzle 152 engages the top plate, morespecifically the grid plates 155. The same process is repeated for thebottom nozzles 154 of the fuel assemblies 110, 120 in which the shoulderportions 180 of the bottom nozzles 154 are engaged with the bottom coreplate 230 in a similar manner. This process may be conducted in anyorder or sequence, so that in some instances the bottom flow nozzles 154may first be inserted into the bottom core plate 230 before the top flownozzles 152 are inserted into the top core plate 232. Either approach isacceptable.

The assembly process continues by coupling the top and bottom coreplates 232, 230 together using the plurality of connecting rods 234 and236 (where used) extending between the core plates 230,232 as describedabove. The threaded ends of the connecting rods 234, 236 are insertedthrough the holes 251 and the central mounting brackets 253 in the topand bottom core plates 232, 230. The mounting hardware 260 is installedon each connecting rod 234, 236. The nuts of the mounting hardware 260are tightened, which in turn results in drawing the top and bottom coreplates 232, 230 together with the connecting rods. The fuel assemblies110, 120 are compressed between the top and bottom core plates 230, 232to complete the portable nuclear fuel cartridge 1000 assembly process.

The assembled portable nuclear fuel cartridge 1000 defines a compact andversatile nuclear fuel core unit that may be installed in a reactorvessel 500 of any suitable configuration and in any appropriateorientation. FIG. 16 shows the portable nuclear fuel cartridge 1000 inone of many possible installations in a reactor vessel 500. The portablenuclear fuel cartridge 1000 is shown positioned inside a nuclear reactorvessel 500 which is located in a nuclear reactor containment enclosure505 including a wet well. The reactor vessel 500 includes a primarycoolant inlet/outlet nozzle 510 and a removable nuclear reactor vesselhead 520 which provides access to an interior cavity 515 of the nuclearreactor vessel 500 configured for receiving and supporting the portablenuclear fuel cartridge 1000, as shown. In one embodiment, the portablenuclear fuel cartridge 1000 may be positioned in a riser pipe 525disposed inside the reactor vessel 500; however, other suitable mountingarrangements may be used. In one embodiment, the fuel cartridge 1000 maybe oriented vertically and primary coolant in the reactor vessel mayflow upwards through the fuel cartridge 1000 and reactor core fuelassemblies 110, 120 entering the bottom core plate 230 and leaving thetop core plate 232. The primary coolant is heated as it flows throughthe fuel assembly core 100 in passing by the fuel rods 111 in a mannerwell known in the art. The primary coolant in the reactor vessel 500enters the bottom core plate 230 and a bottom nozzle 254 of the fuelassemblies 110, 120, flows in parallel along the fuel rods 111, andexits the top nozzle 252 and top core plate 232. It will be appreciatedthat in some embodiments, the partial fuel assemblies 120 may optionallybe omitted.

Methods of Fueling a Nuclear Reactor

Referring now to FIG. 16, a method of fueling a nuclear reactor 500according to the present invention will be described. While theinventive method is described below in conjunction with the portablenuclear fuel cartridge 1000 described above, it is to be understood thatthe method is not so limited in al embodiments and different structuralembodiments of a portable nuclear fuel cartridge can be utilized.

The method may include: opening a reactor vessel 500 defining aninterior cavity 515; loading the fuel cartridge 1000 into the cavity515; and closing the reactor vessel 500. Because the fuel cartridge 1000comprises an integrated fuel core 100, there is no need to manipulateand handle individual fuel assemblies 110 or 120 on site when initiallyfueling the reactor vessel 500. The entire fuel cartridge 1000 is merelylifted and transported to the reactor vessel 500 and then inserted orplugged into the reactor vessel 500 after removing the nuclear reactorvessel head 520 from the nuclear reactor vessel body. The top headclosure 220 is then re-closed. If a spent fuel cartridge 1000 is inplace in the reactor, this spent unit would first be removed from thereactor vessel 500 to make room for the new fuel cartridge 1000.Advantageously, the fuel cartridge 1000 with all of the fuel assemblies110, 120 installed may be assembled outside of the reactor vessel 500and containment enclosure, either elsewhere on site or off site. Sincethe fully assembled and complete fuel cartridge 1000 is ready to go, theduration of a refueling outage may be greatly reduced thereby savinglabor, time, and financial resources.

Another method of fueling a nuclear reactor will now be described, inwhich the method comprises: a) opening a nuclear reactor vessel; b)moving a nuclear fuel cartridge from a position outside of the nuclearreactor vessel to a position within an interior cavity of the nuclearreactor vessel, the nuclear fuel cartridge comprising a unitary supportstructure, and a plurality of nuclear fuel assemblies arranged tocollectively form a fuel core, the fuel core mounted in the unitarysupport structure; and c) closing the nuclear reactor vessel. Thenuclear fuel cartridge is moved as a single unit.

The step of opening the nuclear reactor vessel may include setting awater level in a reactor containment enclosure to allow access to headbolts that secure a nuclear reactor vessel head to a nuclear reactorvessel body, removing the head bolts, and raising the water level andremoving the nuclear reactor vessel head from the nuclear reactor vesselbody to provide an opening into the interior cavity of the nuclearreactor vessel.

The step of opening the nuclear reactor vessel may comprise removing anuclear reactor vessel head from a nuclear reactor vessel body toprovide an opening into the interior cavity of the nuclear reactorvessel. The step of moving the nuclear fuel cartridge may compriselowering the nuclear fuel cartridge into the nuclear reactor vesselbody. The step of closing the nuclear reactor vessel may comprisesecuring the nuclear reactor vessel head to the nuclear reactor vesselbody to enclose the opening into the interior cavity.

In certain embodiments, the step of moving the nuclear fuel cartridgemay further comprise coupling a crane to the unitary support structureof the nuclear fuel cartridge, lifting the nuclear fuel cartridge withthe crane, lowering the nuclear fuel cartridge into the nuclear reactorvessel body with the crane, and uncoupling the crane from the unitarysupport structure of the nuclear fuel cartridge. Coupling the crane tothe unitary support structure may comprise coupling the crane to alifting ring of the unitary support structure.

The fuel core of the nuclear fuel cartridge may comprise all nuclearfuel assemblies used to operate the nuclear reactor for a cycle life,which may be greater than 24 months in certain embodiments. During themoving step, the unitary support structure is sufficiently strong toenable handling of the nuclear fuel cartridge within a margin of safetyrequired by ANSI 14.6 (1993).

Methods of Defueling a Nuclear Reactor

Referring now to FIGS. 17 to 36, a method of defueling a nuclear reactor500 according to the present invention will be described. While theinventive method is described below in conjunction with the portablenuclear fuel cartridge 1000 described above, it is to be understood thatthe method is not so limited in al embodiments and different structuralembodiments of a portable nuclear fuel cartridge can be utilized.

In one embodiment, the method of defueling a nuclear reactor comprises:a) opening a nuclear reactor vessel; b) removing a nuclear fuelcartridge from an interior cavity of the nuclear reactor vessel, thenuclear fuel cartridge comprising a unitary support structure, and aplurality of nuclear fuel assemblies arranged to collectively form afuel core, the fuel core mounted in the unitary support structure; andc) submerging the nuclear fuel cartridge within a spent fuel pool.

With reference to FIG. 17, in certain embodiments the step of openingthe nuclear reactor vessel 500 may include setting a water level 700 ina reactor containment enclosure 505 to allow access to head bolts 501that secure a nuclear reactor vessel head 520 to a nuclear reactorvessel body 530. Removing the head bolts 501. An open transfer cask 800,which includes an open multi-purpose canister 900 therein, may also besubmerged in the spent nuclear fuel pool 710 at this time.

With reference now to FIG. 18, the water level 700 is then raised. Withreference now to FIG. 19, and the nuclear reactor vessel head 520 isremoved from the nuclear reactor vessel body 530 to provide an opening535 into the interior cavity 515 of the nuclear reactor vessel 500. Withreference now to FIG. 20, the control rod drive internals 575 areremoved from the nuclear reactor vessel 500 and placed in the spent fuelpool 710. A crane (or other lifting mechanism) is then coupled to theunitary support structure 200 of the nuclear fuel cartridge 1000 (FIG.21), which is located within the nuclear reactor vessel 500 as describedabove. In one embodiment, the crane is coupled to the lifting ring 270of the unitary support structure 200. The nuclear fuel cartridge 1000 isthen lifted out of the interior cavity 515 of the nuclear reactor vessel500 with the crane. It should apparent from the above that the nuclearfuel cartridge 100 is removed from the nuclear reactor vessel 500 as asingle unit.

With reference now to FIGS. 22A-B concurrently, the nuclear fuelcartridge 1000 is then lowered into the spent nuclear fuel pool 710 andlowered into the cavity 905 of the open multi-purpose canister 900. Asmentioned above, the open multi-purpose canister 900 may be positionedwithin an open transfer cask 800 at this time. 97. The nuclear fuelcartridge 1000 is lowered/submerged into the spent fuel pool 710 as asingle unit.

With reference now to FIG. 23, once the nuclear fuel cartridge is withinthe multi-purpose canister 900, the multi-purpose canister 900 is closedby positioning a canister lid 910 in place. With reference now to FIG.24, the open cask 800 and closed canister 900 are then lifted from thespent fuel pool 710. The closed multi-purpose canister 900 is thenprepared for dry storage. In one embodiment, this preparation includesdraining bulk water from the closed multi-purpose canister 900, flowinga non-reactive gas through the closed multi-purpose canister 900 toachieve a level of dryness within the multi-purpose canister 900suitable for dry storage, backfilling the closed multi-purpose canister900 with a non-reactive gas, and sealing the closed canister. As aresult of the above, the unitary support structure 200 of the nuclearfuel cartridge 1000 serves as a fuel basket within the multi-purposecanister 900. The multi-purpose canister 900, along with its load of thenuclear fuel cartridge 1000 is now ready for further transport andstorage in a ventilated storage cask.

With reference now to FIG. 25, the ventilated storage cask 1100 isprepared for receiving the loaded multi-purpose canister 900. Initially,the flue extensions 1101 of the ventilated storage cask 1100 are removedto access the lid lifting features. With reference to FIG. 26, the lid1102 of the ventilated storage cask 1100 is then removed.

With reference now to FIG. 27, a mating device 1200 is put in positionand coupled to the body 1105 of the ventilated storage cask 1100. Withreference now to FIG. 28, a cask transporter 1300 then delivers thetransfer cask 800 (which is loaded with canister 900, which in turn isloaded with the nuclear fuel cartridge 1000) to position above and inalignment with the mating device 1200. With reference now to FIG. 28,the transfer cask 800 is then mated with the mating device 1200.

With reference to FIG. 30, the rigging 1305 is attached to the loadedcanister 900 and the canister 900 is raised slightly. The bottom lid 805of the transfer cask 800 is removed and the mating device 1200 isopened. With reference to FIG. 31, the canister is then lowered into theventilated storage cask 1100. With reference to FIG. 32, the rigging isthen disconnected. With reference to FIG. 33, the transfer cask 800 isreconnected to the cask transporter 1300 and the mating device 1200 isclosed. The transfer cask 800 and mating device 1200 are then removedand the lid 1102 and vents 1101 of the ventilated storage cask 100 arereplaced.

While the foregoing description and drawings represent exemplaryembodiments of the present invention, it will be understood that variousadditions, modifications and substitutions may be made therein withoutdeparting from the spirit and scope and range of equivalents of theaccompanying claims. In particular, it will be clear to those skilled inthe art that the present invention may be embodied in other forms,structures, arrangements, proportions, sizes, and with other elements,materials, and components, without departing from the spirit oressential characteristics thereof. In addition, numerous variations inthe methods/processes. One skilled in the art will further appreciatethat the invention may be used with many modifications of structure,arrangement, proportions, sizes, materials, and components andotherwise, used in the practice of the invention, which are particularlyadapted to specific environments and operative requirements withoutdeparting from the principles of the present invention. The presentlydisclosed embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingdefined by the appended claims and equivalents thereof, and not limitedto the foregoing description or embodiments. Rather, the appended claimsshould be construed broadly, to include other variants and embodimentsof the invention, which may be made by those skilled in the art withoutdeparting from the scope and range of equivalents of the invention.

What is claimed is:
 1. A nuclear reactor core comprising: a plurality offirst nuclear fuel assemblies, each of the plurality of first nuclearfuel assemblies having a first transverse cross-sectional configuration,the plurality of first nuclear fuel assemblies arranged in a rectilinearpattern defining peripheral corner regions; a plurality of secondnuclear fuel assemblies, each of the plurality of second nuclear fuelassemblies having a second transverse cross-sectional configuration thatis different than the first transverse cross-sectional configuration;and wherein the plurality of second nuclear fuel assemblies are disposedwithin the corner regions, the plurality of first and second nuclearfuel assemblies collectively forming a nuclear fuel core.
 2. The nuclearreactor core according to claim 1 further comprising a reflectorcylinder circumferentially surrounding the first and second fuelassemblies.
 3. The nuclear reactor core according to any one of claims 1to 2 wherein each of the plurality of first nuclear fuel assemblies hasa rectangular transverse cross-sectional shape.
 4. The nuclear reactorcore according to any one of claims 1 to 3 wherein each of the pluralityof second nuclear fuel assemblies has a triangular transversecross-sectional shape.
 5. The nuclear reactor core according to any oneof claims 1 to 4 wherein the nuclear fuel core has a polygonaltransverse cross-sectional shape.
 6. The nuclear reactor core to claim 5wherein the polygonal shape is an octagon.
 7. The nuclear reactor coreaccording to any one of claims 1 to 6 wherein the rectilinear patternformed by the plurality of first nuclear fuel assemblies is a modifiedcruciform pattern comprising four symmetric quadrants, each of the fourquadrants comprising two peripheral corner regions.
 8. The nuclearreactor core according to any one of claims 1 to 7 wherein the firsttransverse cross-sectional configuration comprises a first shape and thesecond transverse cross-sectional configuration comprises a secondshape, the first shape being different than the second shape.
 9. Thenuclear reactor core according to any one of claims 1 to 8 furthercomprising: a unitary support structure; the nuclear fuel core mountedwithin the unitary support structure; and wherein the unitary supportstructure and the nuclear fuel core collectively form a nuclear fuelcartridge than can be removed from a reactor vessel as a single unit.10. The nuclear reactor core according to claim 9 wherein the unitarysupport structure comprises a bottom core plate, a top core plate, andone or more longitudinal members interconnecting the top and bottom coreplates together, the nuclear fuel core sandwiched between the top andbottom core plates.
 11. The nuclear reactor core according to claim 10further comprising: each of the top and bottom core plates comprising aplurality of open cells; each of the first and second nuclear fuelassemblies comprising: a top portion that at least partially nestswithin one of the plurality of open cells of the top core plate; and abottom portion that at least partially nests within one of the pluralityof open cells of the bottom core plate.
 12. The nuclear reactor coreaccording to claim 11 wherein each of the plurality of open cells ofboth the top and bottom core plates has a shape which conforms to eitherthe first transverse cross-sectional configuration of the plurality offirst nuclear fuel assemblies or the second transverse cross-sectionalconfiguration of the plurality of second nuclear fuel assemblies. 13.The nuclear reactor core according to any one of claims 11 to 12 whereineach of the first and second nuclear fuel assemblies comprises a topnozzle and a bottom nozzle, and wherein for each of the first and secondnuclear fuel assemblies: the top nozzle at least partially nests withinone of the plurality of open cells of the top core plate; and the bottomnozzle at least partially nests within one of the plurality of opencells of the bottom core plate.
 14. The nuclear reactor core accordingto any one of claims 11 to 13 wherein for each of the first and secondnuclear fuel assemblies: the top portion comprises a top shoulderelement that abuts a bottom surface of the top core plate; and thebottom portion comprises a bottom shoulder element that abuts a topsurface of the bottom core plate.
 15. The nuclear reactor core accordingto any one of claims 10 to 14 wherein the one or more longitudinalmembers comprise a plurality of connecting rods extending axiallybetween the top and bottom core plates.
 16. The nuclear reactor coreaccording to claim 15 wherein the plurality of connecting rods comprisea plurality of peripheral connecting rods located outboard of thenuclear fuel core.
 17. The nuclear reactor core according to any one ofclaims 15 to 16 wherein the plurality of connecting rods comprise aplurality of central connecting rods located inboard of the nuclear fuelcore.
 18. The nuclear reactor core according to claim 17 wherein theplurality of central connecting rods are disposed in notched corners ofa modified one of the plurality of first nuclear fuel assemblies. 19.The nuclear reactor core according to any one of claims 9 to 18 whereinthe reflector cylinder is coupled to the unitary support structure andforms part of the nuclear fuel cartridge.
 20. The nuclear reactor coreaccording to any one of claims 9 to 19 wherein the nuclear fuelcartridge is self-supporting and free-standing.
 21. The nuclear reactorcore according to claim 2 wherein the reflector cylinder comprises aplurality of arcuately shaped wall segments coupled together by lapjoints.
 22. The nuclear reactor core according to any one of claims 1 to21 wherein each of the plurality of first nuclear fuel assembliescomprises a control rod assembly configured to control reactivity duringoperation of the nuclear reactor core.
 23. The nuclear reactor coreaccording to any one of claims 1 to 22 wherein each of the plurality ofsecond nuclear fuel assemblies are free of a control rod assembly. 24.The nuclear reactor core according to any one of claims 1 to 23 whereineach of the first and second nuclear fuel assemblies comprise aplurality of nuclear fuel rods.
 25. The nuclear reactor core accordingto claim 24 wherein each of the plurality of first nuclear fuelassemblies comprises X nuclear fuel rods and each of the plurality ofsecond nuclear fuel assemblies comprises Y nuclear fuel rods, wherein Yis less than X.
 26. The nuclear reactor core according to claim 25wherein Y is about one-half X.
 27. A nuclear reactor core comprising: areflector cylinder; a nuclear fuel core disposed within the reflectorcylinder, the nuclear fuel core comprising: a plurality of first nuclearfuel assemblies, each of the plurality of first nuclear fuel assemblieshaving a first transverse cross-sectional shape; and a plurality ofsecond nuclear fuel assemblies, each of the plurality of second nuclearfuel assemblies having a second transverse cross-sectional shape that isdifferent than the first transverse cross-sectional shape.
 28. Thenuclear reactor core according to claim 27 wherein the plurality offirst nuclear fuel assemblies arranged to form a central region of thenuclear fuel core that comprises peripheral corner regions; and whereinthe plurality of second nuclear fuel assemblies are disposed in theperipheral corner regions.
 29. The nuclear reactor core according to anyone of claims 27 to 28 wherein each of the plurality of first nuclearfuel assemblies comprises a control rod assembly configured to controlreactivity during operation of the nuclear reactor core.
 30. The nuclearreactor core according to any one of claims 27 to 29 wherein each of theplurality of second nuclear fuel assemblies are free of a control rodassembly.
 31. The nuclear reactor core according to any one of claims 27to 30 wherein each of the first and second nuclear fuel assembliescomprise a plurality of nuclear fuel rods.
 32. The nuclear reactor coreaccording to claim 31 wherein each of the plurality of first nuclearfuel assemblies comprises X nuclear fuel rods and each of the pluralityof second nuclear fuel assemblies comprises Y nuclear fuel rods, whereinY is less than X.
 33. The nuclear reactor core according to claim 25wherein a ratio of Y:X is in a range of 1:1.5 to 1:3.
 34. The nuclearreactor core according to any one of claims 27 to 33 wherein the firsttransverse cross-sectional shape is rectangular and the secondtransverse cross-sectional shape is triangular.
 35. A portable nuclearfuel cartridge comprising: a unitary support structure; a plurality ofnuclear fuel assemblies arranged to collectively form a fuel core for anuclear reactor, each of the plurality of nuclear fuel assembliescomprising a plurality of nuclear fuel rods; and the fuel coreintegrated into the unitary support structure to collectively form aself-supporting assemblage than can be lifted as a single unit.
 36. Theportable nuclear fuel cartridge according to claim 35 wherein theunitary support structure comprises: a bottom core plate, a top coreplate, and one or more longitudinal members interconnecting the top andbottom core plates together, the fuel core sandwiched between the topand bottom core plates.
 37. The portable nuclear fuel cartridgeaccording to claim 36 wherein the top and bottom core plates comprise alattice structure.
 38. The portable nuclear fuel cartridge according toany one of claims 36 to 37 wherein each of the top and bottom coreplates comprises a plurality of open cells, each of the plurality ofopen cells of the top and bottom core plates fluidly communicating withat least one of the plurality of nuclear fuel assemblies to form a fluidflow path therethrough.
 39. The portable nuclear fuel cartridgeaccording to claim 38 wherein each of the plurality of fuel assembliesis sized and/or shaped so as to be incapable of being removed from theself-supporting assemblage through the open cells of the top and bottomcore plates with which it is in fluid communication.
 40. The portablenuclear fuel cartridge according to any one of claims 38 to 39 whereineach of the nuclear fuel assemblies comprises: a top portion that atleast partially nests within one of the plurality of open cells of thetop core plate; and a bottom portion that at least partially nestswithin one of the plurality of open cells of the bottom core plate. 41.The portable nuclear fuel cartridge according to claim 40 wherein eachof the first and second nuclear fuel assemblies comprises a top nozzleand a bottom nozzle, and wherein for each of the first and secondnuclear fuel assemblies: the top nozzle at least partially nests withinone of the plurality of open cells of the top core plate; and the bottomnozzle at least partially nests within one of the plurality of opencells of the bottom core plate.
 42. The portable nuclear fuel cartridgeaccording to any one of claims 40 to 41 wherein for each of the firstand second nuclear fuel assemblies: the top portion comprises a topshoulder element that abuts a bottom surface of the top core plate; andthe bottom portion comprises a bottom shoulder element that abuts a topsurface of the bottom core plate.
 43. The portable nuclear fuelcartridge according to any one of claims 36 to 42 wherein the one ormore longitudinal members interconnect the top and bottom core plates ata fixed distance from one another.
 44. The portable nuclear fuelcartridge according to any one of claims 36 to 43 wherein the one ormore longitudinal members comprise a plurality of connecting rodsextending axially between the top and bottom core plates.
 45. Theportable nuclear fuel cartridge according to claim 44 wherein theplurality of connecting rods comprise a plurality of peripheralconnecting rods located outboard of the nuclear fuel core.
 46. Theportable nuclear fuel cartridge according to claim 45 wherein theplurality of peripheral connecting rods are circumferentially arrangedaround a periphery of the self-supporting assemblage.
 47. The portablenuclear fuel cartridge according to any one of claims 44 to 46 whereinthe plurality of connecting rods comprise a plurality of centralconnecting rods located inboard of the nuclear fuel core.
 48. Theportable nuclear fuel cartridge according to any one of claim 47 whereinthe a plurality of central connecting rods are located adjacent acentral axis of the self-supporting assemblage
 49. The portable nuclearfuel cartridge according to any one of claim 48 wherein a central opencell of each of the bottom and top core plates includes mountingbrackets configured to receive the central connecting rods.
 50. Theportable nuclear fuel cartridge according to claim 49 wherein theplurality of central connecting rods are disposed in notched corners ofa modified one of the plurality of nuclear fuel assemblies.
 51. Theportable nuclear fuel cartridge according to any one of claims 35 to 50further comprising a reflector cylinder coupled to the unitary supportstructure and circumscribing the nuclear fuel core.
 52. The portablenuclear fuel cartridge according to claim 51 wherein the reflectorcylinder comprises a plurality of arcuately shaped wall segments coupledtogether by lap joints.
 53. The portable nuclear fuel cartridgeaccording to any one of claims 35 to 52 wherein the nuclear fuelcartridge is free-standing.
 54. The portable nuclear fuel cartridgeaccording to any one of claims 35 to 53 wherein the unitary supportstructure is sufficiently strong to enable handling of the portablenuclear fuel cartridge within a margin of safety required by ANSI 14.6(1993).
 55. The portable nuclear fuel cartridge according to any one ofclaims 35 to 54 wherein at least some of the plurality of nuclear fuelassemblies comprise a control rod assembly configured to controlreactivity during operation of the nuclear reactor core.
 56. Theportable nuclear fuel cartridge according to any one of claims 35 to 55wherein the plurality of nuclear fuel assemblies comprises: a pluralityof first nuclear fuel assemblies, each of the plurality of first nuclearfuel assemblies having a first transverse cross-sectional shape; and aplurality of second nuclear fuel assemblies, each of the plurality ofsecond nuclear fuel assemblies having a second transversecross-sectional shape that is different than the first transversecross-sectional shape.
 57. The portable nuclear fuel cartridge accordingto claim 56 wherein the plurality of first nuclear fuel assemblies arearranged to form a central region of the nuclear fuel core thatcomprises peripheral corner regions; and wherein the plurality of secondnuclear fuel assemblies are disposed in the peripheral corner regions.58. The portable nuclear fuel cartridge according to claim 35 furthercomprising: the unitary support structure comprising: a bottom coreplate; a top core plate; and one or more longitudinal membersinterconnecting the top and bottom core plates together, the fuel coresandwiched between the top and bottom core plates. a reflector cylindercoupled to at least one of the top or bottom core plates by the one ormore longitudinal members.
 59. The portable nuclear fuel cartridgeaccording to claim 58, wherein the reflector cylinder is comprised of aplurality of arcuately shaped wall segments coupled together by lapjoints between the plurality of arcuately shaped wall segments.
 60. Theportable nuclear fuel cartridge according to any one of claims 35 to 59wherein the unitary support structure further comprises a lifting ring.61. A portable nuclear fuel cartridge configured for placement in areactor vessel, the fuel cartridge comprising: top and bottom coreplates at opposing ends of the unitary nuclear fuel cartridge, each ofthe top and bottom core plates including a gridwork defining a pluralityof open cells; a plurality of nuclear fuel assemblies disposed betweenthe top and bottom core plates, each of the plurality of nuclear fuelassemblies including a plurality of fuel rods; and a plurality ofconnecting members extending between and interconnecting the top andbottom core plates together to form a unitary support structure; the topand bottom core plates, the plurality of connecting members, and theplurality of nuclear fuel assemblies collectively defining an assemblagethat is self-supporting outside of the reactor vessel and transportableas a single unit.
 62. The portable nuclear fuel cartridge according toclaim 61 wherein the plurality of nuclear fuel assemblies are sandwichedbetween the top and bottom core plates via the connecting members. 63.The portable nuclear fuel cartridge according to any one of claims 61 to62 wherein the plurality of nuclear fuel assemblies and the plurality ofopen cells of both the top and bottom core plates are mutuallyconfigured in transverse cross section so that the plurality of nuclearfuel assemblies are not completely insertable through the open cells ofthe top or bottom core plates.
 64. The portable nuclear fuel cartridgeaccording to any one of claims 61 to 63 wherein each of the plurality ofnuclear fuels assemblies comprises top and bottom flow nozzles disposedat opposing ends thereof, the top and bottom flow nozzles each includinga stepped portion configured to engage the gridwork of the top andbottom core plates to prevent the nuclear fuel assembly from passingcompletely through the open cells of the top and bottom core plates. 65.The portable nuclear fuel cartridge according to claim 64 wherein eachof the top and bottom flow nozzles comprises an outer insertion endconfigured to extend at least partially into the open cells of the topand bottom core plates respectively and an inner end configured toremain outside of the open cells of the top and bottom core platesrespectively.
 66. The portable nuclear fuel cartridge according to anyone of claims 61 to 65 further comprising a reflector cylindercircumferentially surrounding the first and second fuel assemblies. 67.The portable nuclear fuel cartridge according to claim 66 wherein theconnecting members extend through longitudinal passageways in thereflector cylinder.
 68. The portable nuclear fuel cartridge according toany one of claims 66 to 67 wherein the reflector cylinder comprises aplurality of arcuately shaped wall segments coupled together by lapjoints.
 69. A method of fueling a nuclear reactor, the methodcomprising: a) opening a nuclear reactor vessel; b) moving a nuclearfuel cartridge from a position outside of the nuclear reactor vessel toa position within an interior cavity of the nuclear reactor vessel, thenuclear fuel cartridge comprising a unitary support structure, and aplurality of nuclear fuel assemblies arranged to collectively form afuel core, the fuel core mounted in the unitary support structure; andc) closing the nuclear reactor vessel.
 70. The method according to claim69 wherein step a) further comprises removing a nuclear reactor vesselhead from a nuclear reactor vessel body to provide an opening into theinterior cavity of the nuclear reactor vessel; and wherein step b)further comprises lowering the nuclear fuel cartridge into the nuclearreactor vessel body; and wherein step c) further comprises securing thenuclear reactor vessel head to the nuclear reactor vessel body toenclose the opening into the interior cavity.
 71. The method accordingto claim 70 wherein step b) further comprises: b-1) coupling a crane tothe unitary support structure of the nuclear fuel cartridge; b-2)lifting the nuclear fuel cartridge with the crane; b-3) lowering thenuclear fuel cartridge into the nuclear reactor vessel body with thecrane; and b-4) uncoupling the crane from the unitary support structureof the nuclear fuel cartridge.
 72. The method according to claim 71wherein step b-2) further comprises coupling the crane to a lifting ringof the unitary support structure.
 73. The method according to any one ofclaims 69 to 72 wherein the fuel core of the nuclear fuel cartridgecomprises all nuclear fuel assemblies used to operate the nuclearreactor for a cycle life.
 74. The method according to claim 73 whereinthe cycle life is greater than 24 months.
 75. The method according toany one of claims 69 to 74 wherein during step b), the nuclear fuelcartridge is moved as a single unit.
 76. The method according to any oneof claims 69 to 75 wherein the unitary support structure is sufficientlystrong to enable handling of the nuclear fuel cartridge within a marginof safety required by ANSI 14.6 (1993).
 77. The method according toclaim 69 wherein step a) further comprises: a-1) setting a water levelin a reactor containment enclosure to allow access to head bolts thatsecure a nuclear reactor vessel head to a nuclear reactor vessel body;a-2) removing the head bolts; and a-3) raising the water level andremoving the nuclear reactor vessel head from the nuclear reactor vesselbody to provide an opening into the interior cavity of the nuclearreactor vessel.
 78. The method according to any one of claims 69 to 77wherein each of the plurality of nuclear fuel assemblies comprises aplurality of nuclear fuel rods.
 79. The method according to claim 78wherein the unitary support structure comprises: a bottom core plate, atop core plate, and one or more longitudinal members interconnecting thetop and bottom core plates together, the fuel core sandwiched betweenthe top and bottom core plates.
 80. The method according to claim 79wherein the top and bottom core plates comprise a lattice structure. 81.The method according to any one of claims 79 to 80 wherein each of thetop and bottom core plates comprises a plurality of open cells, each ofthe plurality of open cells of the top and bottom core plates fluidlycommunicating with at least one of the plurality of nuclear fuelassemblies to form a fluid flow path therethrough.
 82. The methodaccording to claim 81 wherein each of the plurality of fuel assembliesis sized and/or shaped so as to be incapable of being removed from theunitary support structure through the open cells of the top and bottomcore plates with which it is in fluid communication.
 83. The methodaccording to any one of claims 69 to 82 further comprising a reflectorcylinder coupled to the unitary support structure and circumscribing thenuclear fuel core.
 84. The method according to any one of claims 69 to83 wherein the fuel core is integrated into the unitary supportstructure to collectively form a self-supporting assemblage that ismoved as a single unit during step b).
 85. A method of defueling anuclear reactor, the method comprising: a) opening a nuclear reactorvessel; b) removing a nuclear fuel cartridge from an interior cavity ofthe nuclear reactor vessel, the nuclear fuel cartridge comprising aunitary support structure, and a plurality of nuclear fuel assembliesarranged to collectively form a fuel core, the fuel core mounted in theunitary support structure; and c) submerging the nuclear fuel cartridgewithin a spent fuel pool.
 86. The method according to claim 85 whereinstep c) further comprises: c-1) positioning an open canister in thespent fuel pool; and c-2) lowering the nuclear fuel cartridge into acavity of the open canister.
 87. The method according to claim 86wherein the open canister is positioned within an open cask.
 88. Themethod according to claim 87 further comprising: d) closing the canisterwith a canister lid; e) lifting the open cask and closed canister fromthe spent fuel pool; and f) preparing the closed canister for drystorage.
 89. The method according to claim 88 wherein step f) furthercomprises: f-1) draining bulk water from the closed canister; f-2)flowing a non-reactive gas through the closed canister to achieve alevel of dryness within the canister suitable for dry storage; f-3)backfilling the closed canister with a non-reactive gas; and f-4)sealing the closed canister.
 90. The method according to any one ofclaims 86 to 89 wherein the unitary support structure serves as a fuelbasket within the canister.
 91. The method according to any one ofclaims 86 to 90 wherein the canister is a multi-purpose canister. 92.The method according to any one of claims 85 to 91 wherein step b)further comprises: b-1) coupling a crane to the unitary supportstructure of the nuclear fuel cartridge; and b-2) lifting the nuclearfuel cartridge out of the interior cavity of the nuclear reactor vesselwith the crane.
 93. The method according to claim 92 wherein step b-1)further comprises coupling the crane to a lifting ring of the unitarysupport structure.
 94. The method according to any one of claims 85 to93 wherein the fuel core of the nuclear fuel cartridge comprises allnuclear fuel assemblies used to operate the nuclear reactor for a cyclelife.
 95. The method according to claim 94 wherein the cycle life isgreater than 24 months.
 96. The method according to any one of claims 85to 95 wherein during step b), the nuclear fuel cartridge is removed as asingle unit.
 97. The method according to any one of claims 85 to 96wherein during step c), the nuclear fuel cartridge is submerged as asingle unit.
 98. The method according to any one of claims 85 to 97wherein the unitary support structure is sufficiently strong to enablehandling of the nuclear fuel cartridge within a margin of safetyrequired by ANSI 14.6 (1993).
 99. The method according to any one ofclaims 85 to 98 wherein each of the plurality of nuclear fuel assembliescomprises a plurality of nuclear fuel rods.
 100. A method of storingspent nuclear fuel, the method comprising: a) removing a nuclear fuelcartridge from an interior cavity of the nuclear reactor vessel, thenuclear fuel cartridge comprising a unitary support structure, and aplurality of nuclear fuel assemblies arranged to collectively form afuel core, the fuel core mounted in the unitary support structure; b)positioning the nuclear fuel cartridge in a multi-purpose canister; andc) positioning the multi-purpose canister in a cask.
 101. The methodaccording to claim 100 wherein the cask is a ventilated storage cask.102. The method according to any one of claims 100 to 101 wherein theunitary support structure serves as a fuel basket within themulti-purpose canister.
 103. A method of assembling a nuclear fuelcartridge comprising: a) positioning a plurality of fuel assembliesbetween top and bottom core plates, each fuel assembly including aplurality of fuel rods and top and bottom flow nozzles at opposing endsthereof; b) coupling the top and bottom core plates together with aplurality of connecting rods extending between the core plates; and c)drawing the top and bottom core plates together with the connectingrods, wherein the fuel assemblies are sandwiched between the top andbottom core plates to form a self-supporting assemblage than can belifted as a single unit.
 104. The method according to claim 103 whereinstep a) further comprises: a-1) partially inserting a first portion ofthe top flow nozzle of each of the plurality of fuel assemblies into anopen cell of the top core plate, wherein a second portion of the topflow nozzle engages the top plate; and a-2) partially inserting a firstportion of the bottom flow nozzle of each of the plurality of fuelassemblies into an open cell of the bottom core plate, wherein a secondportion of the bottom flow nozzle engages the bottom plate.
 105. Themethod according to claim 104 wherein the top and bottom flow nozzlesfuel assemblies are configured so that the top and bottom flow nozzlescannot be completely passed through an open cell of the top or bottomcore plate.
 106. The method according to any one of claims 104 to 105wherein the top and bottom flow nozzles of the fuel assemblies eachinclude a stepped portion configured to engage the top and bottom coreplates.
 107. A nuclear fuel core comprising: a plurality of firstnuclear fuel assemblies, each of the plurality of first nuclear fuelassemblies having a first transverse cross-sectional configuration; anda plurality of second nuclear fuel assemblies, each of the plurality ofsecond nuclear fuel assemblies having a second transversecross-sectional configuration that is different than the firsttransverse cross-sectional configuration.
 108. The nuclear fuel coreaccording to claim 107 wherein the plurality of first nuclear fuelassemblies are arranged to form a central portion of the nuclear fuelcore and the plurality of second nuclear fuel assemblies are arrangedabout the periphery of the central portion.
 109. The nuclear fuel coreaccording to claim 108 wherein the plurality of first nuclear fuelassemblies are arranged in a rectilinear pattern forming peripheralcorner regions, and wherein the plurality of second nuclear fuelassemblies are positioned in the peripheral corner regions.
 110. Thenuclear fuel core according to any one of claims 107 to 110 whereinfirst transverse cross-sectional configuration comprises a rectangularshape and the second transverse cross-sectional configuration comprisesa triangular shape.